Symbian
Symbian Developer Library

SYMBIAN OS V9.4

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Open Font System overview

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Purpose

Provides a framework which allows any kind of font to be used on Symbian OS.

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Architectural relationships

The Open Font System is a framework which allows rasterizer plug-ins to be used by the Font and Bitmap Server. A rasterizer plug-in is a DLL which recognises and reads font files stored in a particular format, and provides character bitmaps to the Font and Bitmap server.

Note that the Open Font System makes it possible to support fonts in any format. Whether or not a particular font file format is supported depends on what rasterizer DLLs, if any, are present on the phone. Symbian provides a TrueType rasterizer freetype.dll with the reference platform, however there are good reasons why this may not be included. For example, to reduce the memory overhead of rasterizer DLLs and font files.

The Open Font System is invisible to clients — once a rasterizer DLL has been written and installed, fonts in the supported format are used in exactly the same way as native Symbian fonts.

Client side requests for fonts are made to the Font and Bitmap server through the Fonts API.


Description

The Open Font System framework consists of four classes: COpenFontRasterizer, COpenFontFile, and COpenFont, and (optionally) the convenience class COpenFontRasterizerContext. A rasterizer DLL is created by deriving a class from the first three of these, and declaring a single exported function in the ordinal 1 position. The purpose of each part of the framework and rasterizer DLL are discussed below.

See also

Using Fonts